Theme Override Not Working - Blank Page

[BRK Brandon]

Hi all. I am attempting to do a Theme Override for specific forums. I edit the forum in ACP, then go to theme Override and select the theme I want to use for that forum. Then I save.. When i go to view the forum on my site, I get a completely blank page. The theme I am attempting to use works fine if I manually change to it via bottom of page. Even if I try to override to the IPS default theme I still get a blank page. Has anyone else experienced this issue?

[Adlago]

Try first clear cache: ACP - System - Support -> Mark ' Something isn't working correctly' and Continue

Then 'Override ...'